Method and apparatus for managing modem sample rates on a digital audio interface within a direct access arrangement circuit

ABSTRACT

An apparatus for managing modem sample rates within a direct access arrangement (DAA) circuit is disclosed. The DAA circuit includes a serial audio interface for providing communications between the DAA circuit and a host computer system. The serial audio interface is capable of operating under multiple serial communication interface standards, such as the AC &#39;97 standard and the HD Audio standard. The DAA circuit also includes means for configuring the serial audio interface to transmit and receive modem samples at an audio sample rate higher than a modem sample rate of modem samples and at a predetermined bit size that is wider than a bit size of the modem samples, such that one bit of each of the modem samples is utilized to indicate the validity of each associated modem samples.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to data communications in general, and inparticular to data communications utilizing direct access arrangementcircuits. Still more particularly, the present invention relates to anapparatus for managing modem sample rates on a digital audio interfacewithin a direct access arrangement circuit.

2. Description of Related Art

A direct access arrangement (DAA) circuit is commonly utilized toconnect an electrical system to a telephone network. A DAA circuit canprovide a communication channel between a host computer system and atip-and-ring telephone line.

Generally speaking, a DAA circuit includes a system-side circuit and aline-side circuit. The system-side circuit communicates with a hostcomputer system via a communication interface. The communicationinterface may provide data and control information between the hostcomputer system and the DAA circuitry. In order to allow datacommunications across a tip-and-ring telephone line, the host computersystem may include dedicated modem hardware to provide the necessarymodem data processing. Alternatively, a “soft” modem can be implementedwithin the host computer system by utilizing hardware resources withinthe host computer system in conjunction with modem software that isbeing executed on the host computer system.

Regardless of the type of modem being implemented, the DAA circuit mustbe configured in a manner such that it is compatible with the serialcommunication interface standard utilized by the host computer system inorder for the DAA to take advantage of the serial communicationinterface of the host computer system. Current serial communicationinterface standards include the Audio Codec '97 (AC '97) standard andthe HD Audio standard.

The AC '97 standard, which is sponsored by the Intel Corporation,provides a uniform interface for computer system audio applications. Thecurrent AC '97 standard is enumerated under the AC '97 ComponentSpecification, revision 2.1 (May 22, 1998). The AC-97 ComponentSpecification provides the details for a controller residing in acomputer system to communicate with a variety of telecommunicationdevices, the pertinent of which is incorporated by reference herein.Some of those telecommunication devices, such as modems, are capable ofusing tip-and-ring telephone lines to communicate with other devicesexternal to the computer system.

The HD Audio standard, which is also sponsored by the Intel Corporation,is an upgrade of the AC '97 standard. The current HD Audio standard isenumerated under the HD Audio Specification, revision 1.0 (2004), thepertinent of which is incorporated by reference herein. Similar to theAC-97 specification, the HD Audio Specification maintains a five-wireaudio interface. However, the HD audio interface is based upon apacket-based protocol rather than a time-division multiplex-basedprotocol.

The present disclosure provides a method and apparatus for managingmodem sample rate on a serial communication interface within a DAAcircuit that is capable of accommodating both the AC '97 standard andthe HD Audio standard.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of the present invention, adirect access arrangement (DAA) circuit is capable of coupling a hostcomputer system to a telephone line while providing isolation betweenthe host computer system and the telephone line. The DAA circuitincludes a serial audio interface for providing communications betweenthe DAA circuit and the host computer system. The serial audio interfacecan operate under multiple serial communication interface standards,such as the AC '97 standard and the HD Audio standard. The DAA circuitalso includes means for configuring the serial audio interface totransmit and receive modem samples at an audio sample rate higher than amodem sample rate of modem samples and at a predetermined bit size thatis wider than a bit size of the modem samples, such that one bit of eachof the modem samples is utilized to indicate the validity of eachassociated modem samples.

All features and advantages of the present invention will becomeapparent in the following detailed written description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention itself, as well as a preferred mode of use, furtherobjects, and advantages thereof, will best be understood by reference tothe following detailed description of an illustrative embodiment whenread in conjunction with the accompanying drawings, wherein:

FIG. 1 is a block diagram of a direct access arrangement (DAA) circuit,in accordance with a preferred embodiment of the present invention;

FIG. 2 is a detailed block diagram of the DAA from FIG. 1, in accordancewith a preferred embodiment of the present invention;

FIG. 3 is a detailed block diagram of a programmable serial audiointerface within the DAA from FIG. 1, in accordance with a preferredembodiment of the present invention; and

FIG. 4 is a graphical illustration of a modem sample format accepted bythe programmable serial audio interface from FIG. 3, in accordance witha preferred embodiment of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Referring now to the drawings and in particular to FIG. 1, there isdepicted a block diagram of a direct access arrangement (DAA) circuit,in accordance with a preferred embodiment of the present invention. Asshown, a DAA circuit 10 includes a system-side circuit 11 and aline-side circuit 12. DAA circuit 10 also includes an isolation barrier13 to provide electrical isolation as required by various domestic andforeign governmental standards to isolate a telephone line network froman electrically powered circuitry. System-side circuit 11 includesintegrated circuits and/or discrete devices that are located on thesystem side of an isolation barrier 13. Line-side circuit 12 includesintegrated circuits and/or discrete devices that are located on thetelephone line side of isolation barrier 13. DAA circuit 10 provides acommunication channel from a host computer system 14 to tip-and-ringtelephone lines 15. Host computer system 14 can be any of a wide rangeof electrical systems including, but not limited to, a personalcomputer, a point-of-sale device, a set-top box, etc.

System-side circuit 11 communicates with host computer system 14 througha communication interface (not shown). The communication interface mayprovide data and control information between host computer system 14 andDAA circuit 10. Host computer system 14 may include dedicated modemhardware to provide the necessary modem data processing to allow datacommunications across tip-and-ring telephone lines 15. Alternatively,host computer system 14 may implement a “soft” modem by utilizing systemhardware resources in conjunction with modem software that is beingexecuted within host computer system 14.

With reference now to FIG. 2, there is depicted a detailed block diagramof DAA 10, in accordance with a preferred embodiment of the presentinvention. As shown, a system-side circuit 11 includes a clock interface22, a digital signal processor 24, a programmable serial audio interface25 and an isolation interface 26. Line-side circuit 12 includes a hybridand DC termination circuit 21, a control signal circuit 23 and anisolation interface 28. Control signal circuit 23 may include a ringdetect circuit, an off-hook detect circuit, etc. A group of signal lines29 may couple line-side circuit 12 to discrete components that are usedto connect line-side circuit 12 to the tip-and-ring telephone lines of aconventional telephone network. An isolation barrier 13 is connectedbetween system-side circuit 11 and line-side circuit 12. Isolationbarrier 13 can be capacitors, transformers, opto-couplers, etc.

System-side circuit 11 may communicate with a main bus of a hostcomputer system through programmable serial audio interface 25.Programmable serial audio interface 25 may be configured for any of awide variety of communication interface standards, such as theabove-mentioned AC '97 standard and the HD Audio standard. Programmableserial audio interface 25 is configured as a multi-line bus connection.Information provided across programmable serial audio interface 25 maybe input data, output data, clocking information, synchronizationinformation, reset triggers, etc. In addition to communication with themain bus of the host computer system through programmable serial audiointerface 25, system-side circuit 11 also receives a master clock fromthe host computer system. Although not shown, system-side circuit 11 mayalso communicate with the host computer system through other circuitmodules that provide functionality such as device identification,general purpose input/output, etc.

Referring now to FIG. 3, there is depicted a detail block diagram ofprogrammable serial audio interface 25, in accordance with a preferredembodiment of the present invention. As shown, programmable serial audiointerface 25 includes a detector 31, an AC-97 circuit 32, an HD Audiocircuit 33 and other DAA circuitry 39. Multiple communication interfacelines 40, which includes a SYNC line 41, a BIT_CLK line 42, a RESET line43, a SDATA_OUT line 44 and a SDATA_IN line 45, are provided toprogrammable serial audio interface 25. More particularly, communicationinterface lines 40 are provided to AC-97 circuit 32 and HD Audio circuit33 within programmable serial audio interface 25.

SYNC line 41 is for transmitting a data framing signal that is used toidentify data communication frames. BIT_CLK line 42 is for transmittingcontrol data on SDATA_IN line 45 and latch data on SDATA_OUT line 44.RESET line 43 is for transmitting a hardware reset signal. SDATA_OUTline 44 provides data from a host computer system to DAA circuit 10, andSDATA_IN line 45 provides data from DAA circuit 10 to the host computersystem. Detector 31 counts the number of pulses of BIT_CLK signal onBIT_CLK line 42 during an assertion of SYNC line 41 to determine if hostcomputer system 14 (from FIG. 1) is an AC-97 based system or an HD Audiobased system.

AC-97 circuit 32 may include a serial-to-parallel converter circuit tochange the serial information contained on SDATA_OUT line 44 to parallelinformation that are more suitable to a parallel bus 34. Thus, AC-97circuit 32 may extract the AC 97 field, data, and control informationand, in turn, presents such information on parallel bus 34. Likewise, HDAudio circuit 33 may include a serial-to-parallel converter circuit tochange the serial information contained on SDATA_OUT line 44 to parallelinformation that are more suitable to a parallel bus 35. HD Audiocircuit 33 may extract the serial HD Audio based information and, inturn, presents such information on parallel bus 35. Information that isbeing provided from host computer system 14 (from FIG. 1) throughprogrammable serial audio interface 25 to the rest of DAA circuit 10 isprovided on a bus 36.

AC-97 circuit 32 and HD Audio circuit 33 may also receive informationthat is to be communicated from DAA circuit 10 to host computer system14. Such information are provided on a bus 37 and is converted to theappropriate serial format by either AC-97 circuit 32 or HD Audio circuit33 that provide the serial data through a multiplexer 38 to SDATA_INline 45.

A serial audio interface within a host computer system, such as hostcomputer system 14, is originally designed for processing audio samplesaccording to industry-defined audio standards such as the AC '97 or theHD Audio standard. Thus, the serial audio interface typically cannot beused to process modem samples, especially when the sample rates of modemsamples are generally much smaller than the sample rates of audiosamples. For example, common sample rates for modem samples typicallyinclude 7,200 Hz, 8,000 Hz, 8228.57 (57,600/7) Hz, 8,400 Hz, 9,000 Hz,9,600 Hz and 10,285.71 Hz. In contrast, common sample rates for audiosamples typically include 44.1 kHz and 22.05 kHz. Thus, most, if notall, of the sample rates for audio samples do not match up with thesample rates for modem samples. In addition, the standard sample sizefor modem samples is different from the standard sample size for audiosamples. For example, the standard sample size for modem samples is 16bits, and the standard sample size for audio samples can be either 16 or24 bits. Hence, certain modifications to programmable serial audiointerface 25 are necessary in order for programmable serial audiointerface 25 to communicate with a serial audio interface within a hostcomputer system for the purpose of processing modem samples.

In accordance with a preferred embodiment of the present invention,programmable serial audio interface 25 is configured for a sample widthof 24 bits, with the 16 least significant bits (LSBs) utilized to handlemodem sample data, and one of the 8 most significant bits (MSBs)utilized to indicate the validity of the modem sample data. Withreference now to FIG. 4, there is a graphical illustration of a modemsample format accepted by programmable serial audio interface 25, inaccordance with a preferred embodiment of the present invention. Asshown, a modem sample 50 is 24-bit long. The sixteen LSBs of modemsample 50 is for carrying modem sample data. Any one or more of theeight MSBs of modem sample 50 is for indicating the validity of themodem sample data. For example, any one of the eight MSBs can be set toa logical “1” to indicate the transmitted modem sample is valid, andeither the same or a different one of the eight MSBs can be set to alogical “0” to indicate the transmitted modem sample is invalid.

In addition, when transmitting and receiving modem samples, programmableserial audio interface 25 is set to a sample rate that is at least ashigh as the actual modem sample rate. Basically, the sample rate ofprogrammable serial audio interface 25 can be equal to or higher thanbut not lower than the actual modem sample rate when transmitting andreceiving modem samples. Decimation is required to discard some modemsamples when the sample rate of programmable serial audio interface 25is set to be higher than the actual modem sample rate. However, nointerpolation is allowed to add modem samples when the sample rate ofprogrammable serial audio interface 25 is set to be lower than theactual modem sample rate.

Several examples of modem sample rate management based on theabove-mentioned typical modem sample rates are depicted in Table I.

TABLE I modem sample audio interface rate (Hz) sample rate (Hz) samplepattern 7200 9600 xxx-xxx-xxx- . . . 8000 8000 xxxxxxxx . . . 8228.579600 xxxxxx-xxxxxx- . . . 8400 9600 xxxxxxx-xxxxxxx- . . . 9000 12000xxx-xxx-xxx- . . . 9600 9600 xxxxxxxx . . . 10285.71 24000xxx----xxx----xxx--- . . .In Table I, “x” represents a valid modem sample packet and “-”represents an invalid modem sample packet. In row 1, the sample rate ofprogrammable serial audio interface 25 is set to 9,600 Hz to handle themodem sample rate of 7,200 Hz, and the modem sample pattern is threevalid sample packets followed by one invalid sample packet. In row 2,the sample rate of programmable serial audio interface 25 is set to8,000 Hz to handle the modem sample rate of 8,000 Hz. Because the samplerate of programmable serial audio interface 25 matches with the modemsample rate, there is no invalid modem sample packet. In row 3, thesample rate of programmable serial audio interface 25 is set to 9,600 Hzto handle the modem sample rate of 8,228.57 Hz, and the modem samplepattern is six valid sample packets followed by one invalid samplepacket. In row 4, the sample rate of programmable serial audio interface25 is set to 9,600 Hz to handle the modem sample rate of 8,400 Hz, andthe modem sample pattern is seven valid sample packets followed by oneinvalid sample packet.

In row 5, the sample rate of programmable serial audio interface 25 isset to 12,000 Hz to handle the modem sample rate of 9,600 Hz, and themodem sample pattern resembles those in row 1. In row 6, the sample rateof programmable serial audio interface 25 is set to 9,600 Hz to handlethe modem sample rate of 9,600 Hz, and the modem sample patternresembles those in row 2. In row 6, the sample rate of programmableserial audio interface 25 is set to 24,000 Hz to handle the modem samplerate of 10,285.71 Hz, and the modem sample pattern is three valid samplepackets followed by four invalid sample packets.

As has been described, the present invention provides an apparatus formanaging modem sample rates on a digital audio interface within a DAAcircuit.

While the invention has been particularly shown and described withreference to a preferred embodiment, it will be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention.

1. A method for configuring a direct access arrangement (DAA) circuit,wherein said DAA circuit is capable of coupling a host computer systemto a telephone line while providing isolation between said host computersystem and said telephone line, said method comprising: providing aserial audio interface within said DAA circuit, wherein said serialaudio interface allows for communications between said DAA circuit andsaid host computer system, wherein said serial audio interface iscapable of operating under a plurality of serial communication interfacestandards; and configuring said serial audio interface to transmit andreceive modem samples at an audio sample rate higher than a modem samplerate of said modem samples and at a predetermined bit size that is widerthan a bit size of said modem samples, wherein said predetermined bitsize is 24 bits with M least significant bits of said 24 bits beingutilized to store said modem sample data, and one of N most significantbits utilized to indicate validity of said modem sample data by settingsaid one of N most significant bits of said 24 bits to a first logicalstate to indicate said modem sample data is valid, and by setting saidone of N most significant bits of said 24 bits to a second logical stateto indicate said modem sample data is invalid, wherein M and N areintegers greater than one with M being greater than N.
 2. The method ofclaim 1, wherein one of said plurality of serial communication interfacestandards is the AC '97 standard.
 3. The method of claim 2, wherein oneof said plurality of serial communication interface standards is the HDAudio standard.
 4. The method of claim 1, wherein said predetermined bitsize is
 24. 5. The method of claim 1, wherein method further includesconfiguring said serial audio interface to transmit and receive modemsamples at an audio sample rate higher than a modem sample rate of saidmodem samples.
 6. A direct access arrangement (DAA) circuit capable ofcoupling a host computer system to a telephone line while providingisolation between said host computer system and said telephone line,said DAA circuit comprising: a serial audio interface for providingcommunications between said DAA circuit and said host computer system,wherein said serial audio interface is capable of operating under aplurality of serial communication interface standards; and means forconfiguring said serial audio interface to transmit and receive modemsamples at an audio sample rate higher than a modem sample rate of saidmodem samples and at a predetermined bit size that is wider than a bitsize of said modem samples, wherein said predetermined bit size is 24bits with M least significant bits of said 24 bits being utilized tostore said modem sample data, and one of N most significant bits of said24 bits being utilized to indicate validity of said modem sample data bysetting said one of N most significant bits of said 24 bits to a firstlogical state to indicate said modem sample data is valid, and bysetting said one of N most significant bits of said 24 bits to a secondlogical state to indicate said modem sample data is invalid, wherein Mand N are integers greater than one with M being greater than N.
 7. TheDAA circuit of claim 6, wherein one of said plurality of serialcommunication interface standards is the AC '97 standard.
 8. The DAAcircuit of claim 7, wherein one of said plurality of serialcommunication interface standards is the HD Audio standard.
 9. The DAAcircuit of claim 6, wherein said predetermined bit size is
 24. 10. TheDAA circuit of claim 6, wherein DAA circuit further includes means forconfiguring said serial audio interface to transmit and receive modemsamples at an audio sample rate higher than a modem sample rate of saidmodem samples.